This invention relates to a process and a device for drawing off a milk sample from a milk conveyor pipe and equipment for drawing off a sample, particularly on milk collection lorries.
The demands made of automatic equipment for taking milk samples are high. The equipment must function perfectly so that carry-over errors are minimal and samples are taken in the correct quantitative proportion. A quality-payment system, where milk samples are taken by hand with a ladle and mixer is not above all doubt since carry-over errors may, for example, occur or there may be a delay between taking the sample and collecting the milk.
After each sampling process, a certain amount of milk remains as liquid which adheres and accumulates on the wetted inner surfaces of the automatic sampling equipment. This remaining milk is rinsed away again by the next sampling process, is mixed with the following milk and partially carried into the sample bottle as a so-called carry-over. Carry-over errors can be minimized by means of special measures relating to the construction and technical functioning of automatic milk sampling equipment
Moreover, it is important that representative samples are taken, a representative sample being a portion of the milk whose features correspond to that of the whole quantity from which the sample is taken. It is also possible by means of measures relating to the construction and technical functioning, to keep the representativity high.
One known embodiment of a device for the direct transfer of partial quantites of milk from a milk conveyor pipe into a sample bottle is disclosed in the German published patent application DE 36 27 849. This device functions such that a sample bottle is affixed to a peripheral opening in the milk conveyor pipe in an airtight manner using a flexible sealing part so that there is form and/or force locking. A fill-up syringe and an air-discharge syringe are disposed in the conveyor pipe and are movable transverse to the conveyor pipe and can be inserted into the sample bottle to take up a position for drawing off a sample. Prior to insertion in the sample bottle, the syringes are in the so-called rinse position in the milk flow of the conveyor pipe. By means of a shutting element which also projects into the milk conveyor pipe and is diposed such that it is movable therein, the timing of the sampling can be controlled. The disadvantages of this known construction are in the movable parts which are difficult to clean in the milk conveyor pipe, and which also give rise to problems of airtightness. If a vacuum occurs when conveying the milk in the milk conveyor pipe, milk from the sample bottle can flow back into the milk conveyor pipe. This impairs representative sampling.
Another known embodiment of a device for drawing off milk samples is disclosed in the German published patent application DE 35 02 858. The device comprises a draw-off pipe, inserted into the milk conveyor pipe, through which milk is drawn off into the sample bottle by means of a hose pump driven by rhythmic impulses. According to the expected quantity of milk, the length and/or frequency of the impulses can be changed in order to achieve a representative sample. Milk can be prevented from being carried over from a previous sampling to the next sample by automatically activating the sample draw-off pipe for a short time as soon as the conveyor pipe is filled with milk, in order to rinse the milk draw-off pipe free of remaining adhering milk, this rinse milk being led away and not taken into the sample bottle. Disadvantageous additional structural expenditure is required by this device to activate the sample draw-off pipe and to capture the rinse milk, for which a funnel is used.